1. Field of the Invention
The present invention relates to tape speed controls for magnetic tape transports. More specifically, the present invention is directed to a tape speed control using clock signals synthesized from a playback data train.
2. Description of the Prior Art
In digital magnetic recording apparatus, the input data is recorded as flux changes on a magnetic tape medium. In order to faithfully reproduce the recorded digital data, the instantaneous tape speed during playback must be equal to the tape speed used during recording. A speed control servo system is used to control the tape speed during playback utilizing a feedback signal from the tape which is compared with a fixed frequency reference signal to generate an error signal for correcting the tape speed by controlling the tape drive. In multi-channel recording on a plurality of recording tracks on a magnetic tape, the feedback signal is recorded as a reference frequency on one channel, a so-called clock track, while data is being recorded on the other channels. During playback a separate magnetic playback head is used to reproduce the reference frequency from the clock track for use by the speed control system during playback. Such a control system requires the dedication of a recording channel to record the reference frequency or clock signal. In a high density digital recording apparatus where a high packing density is necessary in order to record a large amount of input data supplied at a high rate, data is usually recorded simultaneously on a number of parallel channels on the magnetic tape, and the clock track occupies a channel that could advantageously be used as a data track or channel. Accordingly, it would be advantageous to utilize a tape speed control system that was capable of synthesizing a clock signal from the reproduced data without having to dedicate a recording channel for recording a clock signal.